fix problems with test/sema/Cocoa.m etc on non-apple machines.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@43067 91177308-0d34-0410-b5e6-96231b3b80d8

Driver/Targets.cpp

@@ -55,8 +55,12 @@ namespace {
 class DarwinTargetInfo : public TargetInfoImpl {
 public:
   virtual void getTargetDefines(std::vector<char> &Defs) const {
+// FIXME: we need a real target configuration system.  For now, only define
+// __APPLE__ if the host has it.
+#ifdef __APPLE__
     Define(Defs, "__APPLE__");
     Define(Defs, "__MACH__");
+#endif
     
     if (1) {// -fobjc-gc controls this.
       Define(Defs, "__weak", "");